9ni steel plate for ship lng storage tank with high strength and low yield ratio and its production method

Abstract

The invention relates to a 9Ni steel plate for ship LNG storage tank with high strength and low yield ratio. According to the mass percentage, the chemical constituents are C: 0.02-0.05%, Si: 0.10-0.30%, Mn: 0.50-0.80%, Ni: 8.90-9.50%, P: ≤0.0070%, s: ≤0.0020%, Cr: 0.10-0.25%, Alt: 0.010-0.035%, Nb: 0.010-0.020%, Ca: 0.0005-0.0030%, O: ≤0.0012%, N: ≤0.004%, H: ≤0.00015%, and the balance is Fe and unavoidable impurity elements. The production process flow is: smelting in a converter or electric furnace→RH vacuum degassing→LF refining→RH high vacuum degassing→Ca Treatment→continuous casting→slab slow cooling treatment→slab surface cleaning→heating→rolling→quenching→tempering. For the 9Ni steel, especially the 9Ni thin steel plate, the invention adopts the constituents design of low C, 9% Ni, addition of Nb and Cr. The steel plate is subject to high-temperature hot rolling, and then QLT heat treatment process to obtain 9Ni steel with good strength, toughness and low yield ratio.